TY - JOUR
T1 - MOBSTER - VII. Using light curves to infer magnetic and rotational properties of stars with centrifugal magnetospheres
AU - Berry, I. D.
AU - Shultz, M. E.
AU - Owocki, S. P.
AU - Ud-Doula, A.
N1 - Funding Information:
The authors thank Jason Grunhut for providing the MOST data for HD 142184. The authors thank their colleagues in the MOBSTER collaboration for the thoughtful feedback provided during internal review. MES acknowledges the financial support provided by the Annie Jump Cannon Fellowship, supported by the University of Delaware and endowed by the Mount Cuba Astronomical Observatory. AuD acknowledges support by NASA through Chandra Award number TM1-22001B and GO2-23003X issued by the Chandra X-ray Observatory 27 Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-03060. SPO and AuD acknowledge support from NASA ATP grant 80NSSC22K0628.
Publisher Copyright:
© 2023 The Author(s).
PY - 2023/8/1
Y1 - 2023/8/1
N2 - Early-type B stars with strong magnetic fields and rapid rotation form centrifugal magnetospheres (CMs), as the relatively weak stellar wind becomes magnetically confined and centrifugally supported above the Kepler co-rotation radius. CM plasma is concentrated at and above the Kepler co-rotation radius at the intersection between the rotation and magnetic field axis. Stellar rotation can cause these clouds of material to intersect the viewer's line of sight, leading to photometric eclipses. However, for stars with strong magnetic fields and rapid rotation, CMs can become optically thick enough for emission to occur via electron scattering. Using high-precision space photometry from a sample of stars with strong H α emission, we apply simulated light curves from the rigidly rotating magnetosphere model to directly infer magnetic and rotational properties of these stars. By comparing the values inferred from photometric modelling to those independently determined by spectropolarimetry, we find that magnetic obliquity angle β, viewer inclination i, and critical rotation fraction W can be approximately recovered for three of the four stars studied here. However, there are large discrepancies between the optical depth at the Kepler radius τK expected from magnetometry, and the values required to match the observations. We show that τK of order unity is needed to reasonably match the light-curve morphology of our sample stars.
AB - Early-type B stars with strong magnetic fields and rapid rotation form centrifugal magnetospheres (CMs), as the relatively weak stellar wind becomes magnetically confined and centrifugally supported above the Kepler co-rotation radius. CM plasma is concentrated at and above the Kepler co-rotation radius at the intersection between the rotation and magnetic field axis. Stellar rotation can cause these clouds of material to intersect the viewer's line of sight, leading to photometric eclipses. However, for stars with strong magnetic fields and rapid rotation, CMs can become optically thick enough for emission to occur via electron scattering. Using high-precision space photometry from a sample of stars with strong H α emission, we apply simulated light curves from the rigidly rotating magnetosphere model to directly infer magnetic and rotational properties of these stars. By comparing the values inferred from photometric modelling to those independently determined by spectropolarimetry, we find that magnetic obliquity angle β, viewer inclination i, and critical rotation fraction W can be approximately recovered for three of the four stars studied here. However, there are large discrepancies between the optical depth at the Kepler radius τK expected from magnetometry, and the values required to match the observations. We show that τK of order unity is needed to reasonably match the light-curve morphology of our sample stars.
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U2 - 10.1093/mnras/stad1726
DO - 10.1093/mnras/stad1726
M3 - Article
AN - SCOPUS:85165056309
SN - 0035-8711
VL - 523
SP - 6371
EP - 6385
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 4
ER -